Design of Bend-and-Sweep Compliant Mechanism for Passive Shape Change

Contact aided compliant mechanisms are a class of compliant mechanisms where parts of the mechanism come into contact with one another during motion. Such mechanisms can have nonlinear stiffness, cause stress-relief, or generate non-smooth paths. New contact aided compliant mechanisms called bend-and-sweep compliant mechanisms are presented in this paper. These bend-and-sweep mechanisms are made up of compliant joints which are alternately located in two orthogonal directions, and they also exhibit nonlinear stiffness in two orthogonal directions. The stiffness properties of these mechanisms, in each direction, can be tailored by varying the geometry of the compliant joints. One application of these mechanisms is in the passive wing morphing of flapping wing UAVs or ornithopters. A design study is conducted to understand the effect of hinge geometry on the deflections and maximum von Mises stress during upstroke and downstroke. It is shown that the bend-and-sweep compliant elements deflect as desired in both the bending and sweep directions.